A nonvolatile memory is a kind of memory which is able to store information even in case of power off. Nonvolatile memories have been widely used in portable electronic devices etc, and are holding a larger and larger share in the whole market of memories. Currently, nonvolatile memories in the market still mainly take the form of Flash. However, due to the requirements on storing charge of Flash, it is impossible for the floating gate of Flash to be made thinner infinitely with the development of technologies. It is reported that the limit of flash technology is foreseen to be at about 24 nm, which forces people to search for new kinds of nonvolatile memory with superior performance.
Among these new nonvolatile memories which have already been proposed, there exist a Ferroelectric Random Access Memory (FeRAM), a Magnetic Random Access Memory (MRAM), a Phase Change Random Access Memory (PRAM) and a Resistive Random Access Memory (RRAM), etc, wherein the PRAM and RRAM both differentiate store statuses by detecting the magnitude of current when biasing read voltage. Therefore, they are collectively referred to as resistance-based memories in the industry.
Conventional FeRAMs stores information mainly by means of ferro-polarization in a ferroelectric capacitor. For example, a ferroelectric memory cell has a 1T1C and a 2T2C structure therein (wherein T refers to selection transistor and C refers to ferroelectric capacitor). In the ferroelectric capacitor, a ferroelectric material is served as insulating medium layer of the capacitor, and the FeRAM stores information based on charge variation of this capacitor. Therefore, the area of capacitor cell in conventional FeRAMs is overly large, a reference capacitor cell and a ferroelectric capacitor cannot be downsized at the same rate, making it difficult to form a high-density memory. Moreover, there exists a disadvantage of decrease of device reliability caused by severe destructive readout.